1. Field of the Invention
The present invention relates to an optoelectric converting substrate, and more particularly, to an optoelectric converting substrate having a honeycomb-shaped micro-structured optical waveguide.
2. Description of Related Art
With the development of optical communication technology and optical networking, optical interconnection technology has attracted more and more attention. Compared with the electrical interconnection, transmission over optical lines is much faster. The optical interconnection can be applied to device-to-device links (video to PC) and within computers (e.g. CPU to memory or CPU to CPU connections) for high speed signal transmission. As a result, optoelectric converting substrates have been developed which can enable fast communication between ICs of a multiple chip module (MCM), for example.
Referring to FIG. 6, a sectional view of an optoelectric converting substrate 3 according to U.S. Pat. No. 6,603,915 is shown. An optical waveguide 32 is formed inside a silicon substrate 31 for signal transmission between optoelectronic elements 33 located on the silicon substrate 31. However, to form such a structure, the silicon substrate 31 needs to be etched first, and then a cladding layer 321 and a core layer 322 are sequentially grown on the substrate 31, thereby resulting in a complicated fabrication process. In addition, such technique is incompatible with current fabrication process of the printed circuit boards currently in wide use.
Referring to FIG. 7, a sectional view of an optoelectric converting substrate 4 according to U.S. Pat. No. 6,389,202 is shown. Optical radiation 40 is passed through an optical waveguide 41 and then reflected to an optoelectronic element 43 by a reflecting board inclined at 45 degree relative to the optical waveguide 41. However, such a reflecting board inclined at 45 degree is hard to be fabricated and it is also difficult to optically couple the optical radiation 40 with the optoelectronic element 43. Thus, such a structure is incompatible with current fabrication process of the printed circuit boards as far as optical alignment precision is concerned. In addition, the optoelectronic element 43 in such a structure has limited displacement tolerance in packaging the optoelectric converting substrate 4.
Accordingly, a honeycomb-shaped micro-structured optical waveguide 5 (referring to FIG. 8) can be applied to printed circuit boards to overcome the drawback of the prior art. Although such a structure has been applied in image transmission (referring to Martijn A. Van Eijkelenborg, “Imaging with microstructured polymer fibre”, 2004), it has not yet been applied to the field of printed circuit boards (or substrates).
Referring to FIG. 8, the honeycomb-shaped micro-structured optical waveguide 5 comprises a high-refraction cylinder 51 and a plurality of holes 52. The high-refraction cylinder 51 is made of high temperature resistant plastics and thereby meets the requirements for printed circuit board fabrication. The plurality of holes 52 are honeycomb-shaped and configured to contain air. The refractive index of the high-refraction cylinder 51 is approximately 1.5, and that of air is approximately 1, thus the absolute value of the difference between the two aforesaid refractive indexes is 0.5. The higher the absolute value is, the less is the attenuation of optical transmission in the honeycomb-shaped micro-structured optical waveguide 5. In addition, the smaller the bendable angular radius of the honeycomb-shaped micro-structured optical waveguide 5 is, the easier it is to bend the honeycomb-shaped micro-structured optical waveguide 5. Therefore, the honeycomb-shaped micro-structured optical waveguide 5 can be applied to the optoelectric converting printed circuit boards for optical signal transmission. It should be noted that light is transmitted through the high-refraction cylinder 51 instead of the plurality of holes 52.